Have a question about chute size

[BryanHedstrom]

I just finished a Estes Executioner and I didn't want to use the white plastic parachute. My wife has a sewing machine and I have some ripstop nylon left over from a RC parachutist I made a few years ago so I figured I'd give it a try. I found the chute calc at http://www.vatsaas.org/rtv/systems/Parachutes/Chute.aspx I liked the look so I whipped up a chute a little while ago. It sure looks small, is this style of chute usually smaller than a typical octagonal flat sheet chute? Will this chute work for my Executioner? Here is a screen print of the data I made the chute from:

http://i474.photobucket.com/albums/rr109/BryanHedstrom/ChuteCalcScrnPrnt.jpg

[mkadams001]

I made a couple of these and I thought they were a bit small as well. So, I tested one that was equivalent to an 18" standard nylon parachute with 6 shroud lines. I used a large nose cone that weighed in at 3.4 ounces and did several drop tests down the stairwell in my apartment; the height was around 30'. The standard chute lowered the nose cone slower than this design. I just figured that this design was better suited to really large parachutes and maybe not so practical for small rockets. For a field test I put the chute I made into a Estes Bull Pup and have flown it a couple of times with good results. The Bull Pup with no engine weighs in at 2.1 oz. The decent rate was fine for this rocket. I used a laser engraver to cut the panels which finishes the edges very nicely. When I get a chance I will make another one for a 2 pound rocket and do some more field testing. Good luck.

[hardinlw]

Look on the Fruity Chutes web site for a discussion of the differences between a flat chute and one with a spherical or elliptical shape. The drag coefficient of an elliptical chute is 1.5 and that of a flat one is 0.75. There are two reasons for the difference. An elliptical (or spherical) actually inflates to the specified diameter while a flat chute has a smaller effective diameter. The shape of the inflated elliptical is also more effective at producing drag. The TARC team I mentored used an 18" Fruity Chute for a 17 ounce rocket. Originally they had used the chute from my LOC Viper which I think is 27" and got about the same sink rate. A factor of 2 in CD allows you to drop the diameter by a factor of 0.707 (one divided by the square root of two).